In the fuel tank of a vehicle and the like, there is one wherein a through-hole is formed in an upper wall portion thereof and the like so as to be a fuel circulation opening by fixing a conduction pipe in a state inserted and passed through the through-hole. In an inner end positioned inside the fuel tank of the conduction pipe, there can be connected a filter device, a valve device, and the like (for example, Patent Document 1). In the invention according to the Patent Document 1, a connection pipe forming a casing of the valve device is fitted into the inner end of the conduction pipe, and a locking piece provided to protrude on an outer surface of the inner end of the conduction pipe, and a locking claw provided to protrude on an outer surface of the connection pipe are engaged so as to connect the conduction pipe and the connection pipe. Also, by an L-shaped holding piece provided to protrude on the outer surface of the connection pipe, the locking piece is clamped with respect to the outer surface of the connection pipe so as to make an engagement between the locking piece and the locking claw difficult to be released. However, in a case wherein the conduction pipe and the connection pipe are constructed of resin, the conduction pipe and the connection pipe respectively absorb a fuel and swell (deform), so that there has been a problem that a relative position between the holding piece and the outer surface of the connection pipe is displaced so as to be difficult to maintain an engagement state between the locking piece and the locking claw.
Relative to the above-mentioned problem, there is one wherein the locking piece is clamped with respect to the outer surface of the connection pipe using a ring member which is a separate body from the conduction pipe and the connection pipe (for example, Patent Document 2). The ring member is comparatively difficult to deform even if the ring member swells from a shape thereof so as to be capable of reliably maintaining the engagement state between the locking piece and the locking claw.